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tcbass

What Prop?

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I have a 2000 Cretliner Fishhawk, 17-1/2' foot with a 2000 Mercury 115hp outboard.

It came with a 12.5" aluminum prop with a 23 pitch. I called to order a new aluminum prop and the guy said that prop is way to small.

I just need a general purpose prop for fishing. No skiing or anything.

Is the guy right? Do I have the wrong prop size? If so, what would be the right prop?

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Not sure why he says it's way too small, that's a lot of prop for a 115.  However, if you don't have a tach, anything would be a guess.  Even the prop that's on it.  Look on ebay or Amazon, They make cheap little tachs you can buy for a few bucks that just wraps a wire around a spark plug wire,  If you don't have a tach, Get one of those and see what the motor is turning at WOT and your normal load.  Then you can take most of the guess work out of it.

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I run a Lazer II with the same spec on my Xpress/115 Merc. Hole shot is not impressive, but acceptable. WOT, properly trimmed, I get around 56 mph with myself and gear, with a 1/4 tank of gas.

Get a tach, read your GPS for speed and use a prop slip calculator, that will giv you the true answer.

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Do you know what you were running for WOT RPM's with the old prop? How'd it perform? Did it get out of the hole ok? I was thinking a 23 pitch would be on the big side. Maybe the lower unit gearing is different, but I've got a 17' Ranger with a 130 and I'm split between running a 22 Pitch and a 24 Pitch. My hull weight is 400-500 lbs less so I would think you'd need something smaller. Maybe a 19 or 20? hard to say without knowing what RPM's you're running.

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Thanks guys. He gave me a 13" prop with 21 pitch. He said at WOT it should be around 4,900-5,250 rpms. 

 

 

 

He said to test it out and return it if it's wrong.

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That's fair. Good deal getting to test it out. You might want to check the spec on WOT for that. Seems like it should be higher. I'm not sure though.

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Still beating that same dead horse, but GET A TACH!!! 

That's the ONLY way to properly prop a motor. 

To find the ideal prop, you need a tach and GPS.  You can't use just GPS because a smaller than ideal pitch prop may actually show more speed, but may be over reving the motor.  

 

However, since you are not interested in getting the ideal prop, the one that gives best hole shot, top speed at near the max rpm without over reving the motor, (which ain't gonna happen with an aluminum prop any way) you do need to know what rpm it's turning.

 

Actually, that is the recommend rpm range for that motor, if you have a well calibrated ear.

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